I dealt with IF for years. Did surgeries, IUI, IVFs, had miscarriages, you name it. Finally adopted. Upon adopting DD, my DH asked if I wanted to go back into treatment and try for a second child or adopt a second or what. There was no way I was miraculously cured of IF, and I was not about to spend time in a clinic when I could be playing with my new baby, so treatment was out. Adoption didn't work out for us. Clearly, good old-fashioned luck didn't smile on us either. But by then, I was so incredibly grateful to have ONE child that I decided to concentrate on what I did have and forget about what I didn't have......Because there was nothing I could do to change that.
I had a role model. Years before, my SIL went 10 years in between child #1 and #2. For most of that 10 years, they were trying for #2. Lots of dr. visits, but no real answer as to why they didn't conceive. Just a lot of frustration and pain. Near the end of the 10 year gap, she and I were at the hospital one day, visiting someone. (my mom, I think...) We passed a severely disabled little girl in the lobby. My SIL teared up and said something along the lines of, "What is wrong with me? I have been dwelling on the baby I don't have and what I'm missing when what I should have been doing is thanking God for (insert her DD's name.) She's healthy. That mother (of the disabled little girl) would probably give anything if she could make her little girl healthy like my DD. I ought to just be grateful. From now on, I'm going to concentrate on DD and what I have and not worry about what I don't have. If I get pregnant, I do. If I don't, I don't. I've wasted too much time and energy on that."
She was as good as her word. It was like a load lifted off her. I hate to add to the "she finally got pregnant" stories, but she did.....probably within a year. She had a second DD. My brother was thrilled with both DDs, but had wanted a son as well. Not wanting to take that ride again, they adopted the third child. He came along faster than she could have conceived and delivered, so he was much easier than DD#2.
I don't tell you this to minimize your pain, because it is real. Wanting a second or third baby and not being able to have one hurts. But I promise you, it is emotionally healthier to keep what you have been blessed foremost in your thoughts. That doesn't mean you have to give up trying for another baby. Trust me, I am not a "glass half full" person by nature.

But talking to many other women who have gone through IF, I have found it is a common thread that while they grieve what they long for and do not have, if they keep their focus on the positives in their life (in this case, your 2 children) it keeps them from going into the dark abyss.